Flash memory is an improved version of electrically erasable, programmable read-only memory (EEPROM) which is capable of block-by-block erasing. Flash memory is used in a variety of applications that require programmability with no loss of memory data during power down (non-volatility). Split-gate flash memory cells have been widely used in the semiconductor industry due to low leakage controlled by a word line (WL) or select gate transistor generally comprising doped polysilicon, lower program current, higher endurance and improved data retention.
A particular flash memory cell is known in the art as a split-gate flash cell that comprises 2 side-by-side transistor structures that share a common source (or drain) region that is in the middle of the flash memory cell. In a split-gate flash cell, the select gate is formed to both couple voltage onto the FG and to control a channel region of the transistor. To accomplish these purposes, the select gate is physically formed directly overlying the substrate and overlying, or next to, the FG. Split-gate flash cells are widely used in semiconductor industry due to its advantage (over convention flash cells) of lower leakage controlled by select gate transistor, lower program current, higher endurance and improved data retention.